System and method for determining combustion temperature using infrared emissions

ABSTRACT

The present invention relates to a combustion temperature sensor, and, more particularly, to a combustion temperature sensor that measures infrared energy emitted at several preselected wavelengths from a flame and/or a flame&#39;s hot gas at a turbine inlet location and applies the energy signals to a calculation model to yield temperature.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a combustion temperature sensor,and, more particularly, to a combustion temperature sensor that measuresinfrared energy emitted at several preselected wavelengths from a flameand/or a flame's hot gas at a turbine inlet location and applies theenergy signals to a calculation model to yield temperature. Particularutility for the present invention is in the field of gas turbineengines; although other utilities are contemplated herein.

[0003] 2. Description of Related Art

[0004] Combustion gas turbine designers and users can benefit fromknowledge of flame temperature to determine, for example, NOx and COemission concentrations, flame control, and flame-off conditions.Knowledge of these parameters can be used for increased turbineefficiency, and increased turbine blade life and reliability, as well asdecreased pollution. While much effort has been devoted in the past tothe problem of flame temperature determination, previously developedsystems have been lacking in the ability to come up quickly and reliablywith accurate and useful flame temperature measurements.

[0005] One example of such a temperature measurement system is shown inCashdollar et al., U.S. Pat. No. 4,142,417. This patent discloses an IRmeasuring pyrometer used to calculate both particle and gas temperaturefrom an explosion or fire. In this system three or four IR wavelengthmeasurements (1.57, 2.30, 3.46, and 5.19 um) are obtained to computetemperature of the particles and gas. Significantly, these wavelengthsare chosen to avoid discrete emission bands of gases in the hot flame,e.g., those emission bands which correspond to the quantized energies ofthe vibrational and rotational states of molecules. The wavelengthmeasurements, as provided by Cashdollar et al., are restricted to dustcloud flames which are optically “thick” (i.e., gas cloud flame isoptically opaque at the chosen wavelength), to eliminate the need tocompensate for background radiation. Thus, this system would beincapable of operating in an optically thin environment, such a turbine,since background radiation from the wall on the other side of the flamewould be detected and would destroy any measurement obtained.

[0006] In still other prior art examples, temperature measurement isdetermined by detecting UV radical (e.g., OH, CO, CH, CHO, C, etc.)emission bands in the combustion chamber. For example, German Laid OpenPatent Application DE 4028922/A1 and published PCT Application WO98/07013, each disclose methodologies for temperature determination in acombustion chamber using UV spectral emissions from a variety of gaseousradicals. Radicals, by their very nature, are short-lived as compared tomolecular gas constituents, and thus, determination of temperature frommolecular gas components is more stable. While UV-spectral combustiontemperature determination may be adequate for some purposes, such asystem cannot be used for temperature control at the turbine inletlocation. In addition, UV combustion temperature determination cannotprovide information that can be used to improve turbine blade life andstability.

[0007] It has been proposed (e.g., En Urga Paper 1997) to determinetemperature by observing the entire IR spectrum and directly correlatingcertain radiation intensities of molecular CO₂ and H₂O. However, theharsh operating environment inside the turbine prohibit such a directmeasurement. In addition the cost of producing a fiber optic fiber thatis capable of both transmitting the entire spectrum without degrading inthe harsh operating environment is too prohibitive. Thus, engineeringtrade-offs must be reached between the ability to effectively observeand transmit optical energy signals within a turbine environment, and toobtain appropriate IR wavelength intensities for accurate temperaturemeasurement.

[0008] The present invention solves the aforementioned shortcomings ofthe prior art by selecting an optical fiber and detector that canwithstand the operating environment of a turbine and transmit certain,meaningful wavelengths of optical energy to determine temperature. Morespecifically, the present invention includes improvements in therelationship of the various elements of the optical system to each otherand to the flame. A lens is positioned so that it collects infrared (IR)radiation from that portion of the flame nearest the inlet to theturbine section. The lens focuses the IR energy on one end of an opticalfiber, with a mounting structure supporting one end of the optical fiberin fixed relation to the flame. Compressed air is supplied to themounting structure to shield the lens from combustion gases in theflame. The other end of the fiber is positioned to direct a beam of IRenergy onto a plurality of detectors positioned in a second mountingstructure spaced from the turbine. A spectral separation mechanism isprovided before the detectors to separate the incident IR radiation intoa plurality of narrow-range IR frequencies. An optical choppingmechanism is provided for interrupting the IR beam (at a predeterminedfrequency) before the beam reaches the spectral separating mechanism. Inthis way, the detector receives a chopped, narrow-range IR signal. Thesignals are converted to appropriate electrical signals, processed todetermine optical energy, and preferably compared to a predefinedlook-up table to determine a temperature value for a given set ofdetected optical energy signals.

[0009] It should be emphasized that the disclosure in this applicationincludes “best mode” descriptions of preferred related technologies(e.g., temperature calculation via a look-up table) which are not partof the instant claimed invention. This disclosure is amplified forpurposes of completeness.

SUMMARY OF THE INVENTION

[0010] Accordingly, the present invention provides a system and methodfor determining combustion temperature using infrared emissions. Thepresent invention includes a sensor, a signal conditioning stage and atemperature determining stage to provide temperature measurement at aturbine inlet location.

[0011] In the present invention, an optical system is focused on theflame as the temperature to be measured. As mentioned above, it isdesired to measure the flame temperature when the combustion process isessentially complete, i.e., the gaseous products of combustion containstable compounds of H₂O and CO₂. For this purpose, the IR radiation forthat portion of the flame closest to the turbine inlet is measured. Theresultant optical signal is focused on one end of a fiber optic cableand the other end of the fiber optic cable emits light into an opticaldetection system. This optical detection system includes an opticalchopper, after which the optically chopped signal impinges on a numberof separate detectors which convert the optical signal into an electriccurrent. Each of the optical sensors is preferably provided with aselective filter which passes only a very limited, discrete range (i.e.,narrow band filter) of infrared wavelength. In the preferred embodiment,four wavelength filters are used: one to pass wavelengths of radiationspecifically emitted by CO₂, one to pass wavelengths specificallyemitted by H₂O, one to pass a correlated wavelength of CO₂ and H₂O, andone to pass a background radiation wavelength. The resultant compositesignal is then processed to obtain a stable optical energy signal ateach of the selected wavelengths. Preferably, the signal processingincludes programmable gain amplifiers and digital to analog circuits forpreparation of the signals for computer calculations.

[0012] The IR signals must be fed to an optical detector which issubject to careful temperature control so that temperature effects ofthe detector can be eliminated in so far as is technically feasible. Theoptical chopper causes a zero optical signal to be available at a givenchopping rate (such as 65 Hz) as well as the regular optical signal.Since only the difference between the two signals is used, any DC slowdrift is eliminated. In this case, each channels' programmable gainamplifier is controlled by the computer and the signal processing systemso that the signal remains in the middle A/D range where accuracy isbest. The hardware also includes the use of the digital to analogconverters to generate an offset to the signal to assist in furtherkeeping the A/D conversion accurate.

[0013] A calibration is also performed. The purpose of calibrating theinstrument is to account for component variations from sensor to sensor.Calibration consists of converting an electrical (voltage) signal fromeach detector element, to an optical (radiation) signal which is used inthe software program to determine temperature. A blackbody radiationsource is used for this purpose. Since the amount of radiation exiting ablackbody source is well known, there is a direct relation to thedetector response. A standard instrument blackbody with emissivity ≧0.99has a very well defined spectral emission as a function of itstemperature. Optical radiation, at different blackbody temperatures,transmits through the entire optical system, and the voltage responsefrom each of the four detector elements is measured. The detector outputas a function of uwatts/steradian-cm is then calculated for eachblackbody temperature. These data yield a graph to convert detectorreading to the radiation intensity valued that are necessary for flametemperature back calculation.

[0014] The temperature calculation is performed by using amultidimensional look-up-table (LUT). The LUT is created by thefollowing four steps. (1) A stochastic simulation is carried out tomimic the CO₂ and H₂O concentrations and temperatures over a broad rangeof values, and over the path length present in the turbine. The CO₂concentrations vary from 0.005 to 0.08 mole fraction and H₂O varies from0.005 to 0.16 mole fraction. The temperature is varied over the range ofinterest from 500° C. to 1400° C. (2) The radiation intensities leavingthese simulated paths are calculated using a narrow band model such asRADCAL. (3) Preferably, the resultant intensities are first sorted intoa four dimensional table, with the radiation at each of the threewavelengths arranged in three columns. The temperature corresponding tothe three intensity values are stored in a fourth column, in thefour-dimensional LUT. (4) The sorted values are then averaged to providea convenient number of intensities (typically 8 to 50) along the threedimensions, with temperature forming the fourth dimension. This tableforms the LUT.

[0015] After the LUT is obtained, it is stored into memory. Duringoperation, one of the intensity values is chosen as a backgroundradiation channel and is used to correct the intensities of the other 3wavelengths, and the corrected intensities at these three wavelengthsare used to find the temperature using a sequential search routine. Thissearch is very fast, since the LUT has been sorted in an ascending (ordescending) order. To improve speed, equi-spaced intensities (or thelogarithm of the intensities) with indexing can also be used.

[0016] The details of the various aspects of the system are describedbelow in more detail hereinafter, and are specifically claimed in thecopending application of ______,______ filed on even date herewith.

[0017] It will be appreciated by those skilled in the art that althoughthe following Detailed Description will proceed with reference beingmade to preferred embodiments and methods of use, the present inventionis not intended to be limited to these preferred embodiments and methodsof use. Rather, the present invention is of broad scope and is intendedto be limited as only set forth in the accompanying claims.

[0018] Other features and advantages of the present invention willbecome apparent as the following Detailed Description proceeds, and uponreference to the Drawings, wherein like numerals depict like parts, andwherein:

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a simplified block diagram of the major elements of thesystem of the present invention;

[0020]FIG. 2 is a detailed view of a preferred lens assembly (thepreferred dimensions of the lens are shown in FIG. 2A);

[0021]FIG. 3 is a detailed view of lens mounting and fiber optic cable;

[0022]FIG. 4 is a detailed view of the relationship between the fiberoptic cable, the optical chopper and the IR detector of the presentinvention;

[0023]FIGS. 5A and 5B is a side view and front view, respectively, ofthe preferred IR detector assembly of the present invention;

[0024]FIG. 6 is a block diagram of the preferred embodiment of thesignal conditioning system;

[0025]FIGS. 7A and 7B depict the operational flow of the signalconditioning system of FIG. 6; and

[0026]FIG. 8 is a simplified block diagram of the temperaturecalculation of the present invention; and

[0027]FIG. 9 is a plot of intensity vs. wavelength for several emissionspectra.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] As an overview, FIG. 1, depicts a block diagram representation ofthe major elements which make up the various aspects of the invention. Alens 10 focuses an IR image of a flame whose temperature is to bemeasured onto one end of an optical fiber 12. The other end of the fiberemits the IR radiation through an optical chopper 14 towards a group ofoptical filters 18 and IR detectors 20. The frequency of the opticalchopper 14 is controlled by electronic 16 and the temperature of the IRdetectors is controlled by a temperature controller 22 within a narrow,predetermined range (e.g., 0° C., +/−0.050° C.) to prevent DC voltagedrifts and thermal voltage effects. Temperature controller preferablyincludes a Peltier cooler, although other closed-loop cooling systemsknown in the art are deemed within the scope of the present invention.The electrical output of the IR detectors is fed to a signalconditioning stage 24 to provide a stable optical energy signal for awide range of operating temperatures. The output from the signalconditioning stage is fed into temperature stage 26 to calculate a flametemperature 30. Each of these components of the present invention arediscussed in detail below.

[0029]FIGS. 2 and 2A depict the preferred form of the lens assembly ofthe present invention. The details and preferred dimensions aretabulated in FIG. 2A. Preferably, the lens 10 is composed of Al₂O₃. Towithstand the sever operating environment inside the turbine near thecombustion flame, the mount 50 is preferably formed of Kovar, althoughother materials capable of withstanding the temperatures and pressureswithin a turbine are contemplated. Kovar is preferred when AgCu brazingalloy is used to secure the lens 10 in the mount 50, since Kovar permitsdirect brazing. The preferred lens having the dimensions illustratedwill give a focal length of about 21.27 mm for a wavelength in the IRrange of 2.275-2.885 μm.

[0030] In order to mount the lens 10 in a secure position with respectto the IR input end of a fiber optic cable, the preferred design ofmounting is constructed as schematically illustrated in FIG. 3. As shownthe Kovar lens mount 50 of FIG. 3 is supported on a mount holder 52which, at its rear 54, is connected to an outer lens housing 56 and anoptical fiber mounting fixture 66, thus permitting a predetermined fixedrelationship between lens 10 and the input end 58 of the optical fiber12. This permits the input of the fiber to be positioned in theapproximate focal plane of lens 10 at the IR wavelengths of interest.

[0031] As can be seen, there is a space 55 between the lens mount holder52 and outer mount holder 56. Into this space 55 a supply of highpressure purge air 62 is introduced through air inlet 60. This air isintroduced in a tangential fashion to provided radial andcircumferential flow through space 55. The purge air exits throughfitting 64 which serves also as the mount for the optical system on theside of the turbine combustion chamber, a portion of which is shown at65. This portion is adjacent to the inlet to the turbine (not shown).The IR signal enters the fitting 64 and impinges on the lens 10 where itis focussed on the end 50 of the optical fiber. Since there is aconstant flow of air through fitting 64 into the combustion chamber, noproducts of combustion can flow into space 55 (where such products mightotherwise deposit on the lens 10 resulting in a decrease in IR signalstrength and faulty temperature measurement). For convenience, the highpressure air from the turbine compressor stage (not shown) can be usedas the purge air source and fed into the fitting, although a dedicatedair source is deemed equivalent. This purge air has the dual function ofcooling the lens mount and preventing combustion products fromapproaching the lens.

[0032] The fiber optic cable is preferably formed of Al₂O₃ for the firstmeter (or some predetermined distance away from the intense heat andmechanical stress around the combustion flame), starting at the IR inputend and then continues as As₂ S₃ for another meter. These two fibershave a diameter of about 0.4 mm and are optically aligned at theirjunction and are protected by a fiberglass buffer layer within an outercable sheath 68 of stainless steel.

[0033] At the output end of cable 12, there is provided a cable mountingfixture 72 which suitably secures the cable to the detector housing 74illustrated schematically in FIG. 4. This detector housing supports theoutput end of the cable 12 in position to direct the output IR past anoptical chopper 78 towards the detector assembly 79. As shown, theoptical chopper is placed in the path of the incident radiation betweenthe end of the fiber 12 and the detector 79, and is preferably a tuningfork-type and is driven at 65 Hz by suitable electronics 76.Alternatively, the chopper can be formed with a spinning wheel having aplurality of openings and synchronized (via synchronizing driveelectronics, described below) as a function of rotational velocity.

[0034] The IR detector assembly 79 preferably comprises four separatedetector elements 82 mounted behind four IR filters 80. A more detailed,enlarged plain view of the assembly 79 are shown in FIGS. 5A and 5B. Thedetectors 82 are preferably mounted on Peltier coolers 86 forclosed-loop temperature control of the detectors. Peltier coolers areknown in the art and commercially available. In a preferred embodimentof the invention the detectors 82 are lead sulfide and the four filtershaving the following peak IR transmissions: 2.28 μm (+/−0.005 μm) chosenas a background emission selected to be away from the emission radiationof CO₂ and H₂O; 2.6 μm (+/−0.015 μm) selected as the H₂O emissionwavelength; 2.70 μm (+/−0.015 μm) selected as the CO₂ emissionwavelength; and 2.8 μm (+/−0.005 μm) selected as a combined CO₂ and H₂Oemission wavelength. The spectral plot (wavelength vs. intensity) isshown in FIG. 9, and each of the four emission peaks are indicated inthis figure. Each of these wavelength are depicted The raw electricalsignal from the IR detectors 82 exits through wiring 84.

[0035] Referring now to FIG. 6, a detailed block-diagram representationof the preferred embodiment of the signal conditioning stage 24 of thepresent invention is depicted. Essentially, signal conditioning stage 24consists of a feedback loop utilizing a programmable gain amplifier(PGA) 102, and A/D converter 104 and a digital processor/controller 106.It should be noted at the outset that the circuit shown in FIG. 6 can beduplicated as necessary for each sensor (discussed above), although theA/D converter 104 and the processor/controller 106 are preferablycomprised of multiple input devices (via multiplexing, not shown) thatcan accommodate multiple sensor signal inputs.

[0036] As disclosed above, the sensor 108 (which includes the lens, lenshousing, fiber optic cable, detector, etc.) preferably includes anelectromechanical signal chopper (e.g. an electronically controlledtuning fork, a wheel, etc.) that causes the detector to obtain 2signals: a “dark” signal when the chopper is closed (i.e., no opticalsignal is obtained by the sensor), and a “light” signal when the chopperis open. Preferably, the chopper frequency is set at 65 Hz., althoughother frequencies are envisioned, provided that the associated circuitryshown in FIG. 6 has time to settle between light and dark signals.

[0037] The output signals from the sensor are fed into a programmablegain amplifier (PGA) 102. The PGA preferably includes a differenceamplifier 110 and a programmable gain amplifier 112, and is utilized toadjust signal level as a function of intensity, and to obtain a signaloutput that is in the middle of the operating range of the A/D converter104 to increase overall dynamic range of the system 100. In thepreferred embodiment, the A/D converter 104 has inputs from the PGA 102and the chopper signal synchronizing signal from the signal chopperdrive 14. The output is fed into processor/controller 106.Processor/controller 106 obtains the values of the “light” and “dark”signals and calculates and determines appropriate OFFSET 118 and GAIN120 values, as described below.

[0038] In block diagram form, the preferred operational flow of thesignal conditioning stage 24 is shown in FIG. 7A and 7B. For clarity,corresponding reference numbers of the components of FIG. 6 are omitted.Before the instrument, which includes the sensor 108 and signalconditioning stage 24, is placed in an operating environment, the sensorand associated electronics embodied in FIG. 6 are calibrated 130 (FIG.7A). System calibration 130 is provided to obtain a calibration constant(K) for each system. Those skilled in the art will recognize thatvariations will exist between each component in the instrument (andbetween instruments), and thus, it is desirable to calibrate each systemby determining each system's input/output transfer constant. Thus, eachsystem is measured to determine its operational curve. Optical energy(OE) is related to observed optical voltage (V). Accordingly, an inputoptical signal of a known temperature is input into the system 132. Ablackbody radiation source is preferably used for this purpose, sincethe amount of radiation exiting a blackbody source is well known, therecan obtained a direct relationship with the response of the sensor andassociated electronics. Preferably, a standard blackbody withemissivity >0.99 is used having a well-defined spectral emission as afunction of temperature. Optical radiation, at different blackbodytemperatures, transmits through the sensor 108, and the voltage responsefrom each of the sensors is measured. The detector output(uwatts/steradian-cm) is then calculated for each blackbody temperature.A constant K is determined 134 by observing the output signal as afunction of the input signal (optical energy (OE)−K* input voltage). Itshould be noted that the input/output relationship is not necessarilylinear, and thus, K may reflect a nonlinear curve relating input tooutput. Preferably, several test input values are used to determining aconstant for each input, thus, a calibration curve, not shown, isobtained. The processor/controller stores K 136, to be used incalculating optical energy and temperature, discussed below.

[0039] The operational flow of conditioning an optical input signal fromeach sensor (as described above) at a given wavelength, is shown in FIG.7B, with reference to the system 24 of FIG. 6. From the signal chopperand PGA, the processor/controller obtains the raw values of the “light”signal 142 and the “dark” signal 144, each alternating according to thechopper frequency (e.g. 65 Hz.) synchronized via the A/D converter.Preferably, light and dark signals are obtained at the leading edge andfalling edge of the chopper reference signal, respectively. Each valueis stored by processor/controller for a predetermined time (e.g., 5second buffer memory) to compare current values with previous values.The value of the “dark” signal (background radiation) and the “light”signal are used to calculate an OFFSET value 148, which isdifferentially compared to the chopper signal from the sensor in the PGA152. Preferably, OFFSET value is determined so that a positive value isalways obtained from the PGA. Knowing the amplitude of the signals,processor/controller calculates an appropriate GAIN value 150, andinputs this value to the PGA 154. Preferably, the GAIN dynamicallyadjusts the raw signal value to keep the amplified signal in the“middle” of the A/D converter input voltage range, thereby increasingdynamic range and avoiding saturation. For example, if the operatingvoltage range of the A/D is 0 to 5 V., the gain applied will maintainthe signal value at approximately 2.5 V. The output of the PGA is fedinto the A/D converter and supplied to processor/controller 156. As withthe raw signal values, the gain values can be maintained in buffermemory for a predetermined time. Optical energy (OE) is then calculated158 as a function of input optical intensity (in millivolts) and thecalibration constant K (described above), for each of the fourwavelengths from the sensor. In the preferred embodiment, four opticalenergy output signals 122 are obtained from which temperature isdetermined, as described below.

[0040] To determine temperature, the four optical energy signals areprovided as inputs to a predetermined lock-up table (described below) inwhich temperature is back-calculated using known optical energy vs.temperature model calculations. As shown in FIG. 8, three optical energysignals corresponding to CO₂ and H₂O emission spectra and one backgroundradiation signal (corresponding to the background radiation fromcombustion) 122 are determined, from the above-described process. Thebackground radiation signal is subtracted from each of the other threeemission signals 160, using a correction factor that corrects for filterwidths and relative emissivity at each of the three wavelengths. Thiscorrection factor can be assumed constant (i.e., the relationshipbetween the given wavelengths for any given instrument is fixed, andexhibits little, if any, change as a function of optical energy,temperature, etc.). As shown in the figure, I_(i)′=I_(l)−I_(b) (α);where α=the correction factor, I_(l=), the intensity value at apreselected wavelength (in the preferred embodiment, three wavelengthsare chose, as described above), and I_(b)=the background intensityvalue. The calculation is performed at preferably 3 wavelengths: 2.6 μm(+/−0.015 μm), 2.70 μm (+/−0.015 μm) and 2.8 μm (+/−0.005 μm); withwavelength 2.28 μm (+/−0.005 μm) being used as the background radiationsignal. The three adjusted signals are used as inputs in determiningtemperature from the look-up table.

[0041] The preferred construction of the LUT is described below. Using anarrow-band radiation model, such as provided by commercially availablespectroscopy simulation models (e.g., RADCAL: A Narrow-Band Model forRadiation Calculations in a Combustion Environment, Gossander, WilliamL., NIST Technical Note 1402, April 1993), a simulated calculation ofradiation intensity (at one or more wavelengths) as a function of (1)path length, (2) temperature, and (3) molar concentration of CO₂ and H₂Ois obtained. For the present invention and the intended operatingenvironment, the path length (i.e., the distance between the sensor andthe turbine wall can be assumed to be homogeneous. In addition, it isknown that the temperature range can vary from 900 to 1500 degrees C.,and, for hydrocarbon flames, the molar concentration of CO₂ and H₂O canvary between 0 and 0.075, and 0 and 0.15, respectively. Thus, atemperature range of 800 to 1600 degrees C., and molar concentrationvalues of 0.01 to 0.08 and 0.01 to 0.16 (CO₂ and H₂O, respectively) areused. To improve speed, equi-spaced intensities values (or the logarithmof the intensitites) can be used. Thus, for example, the presentinvention can be adapted to run the calculation using 48 equi-spacedvariable values within the above-noted temperature and concentrationrange. Of course, the present invention can realize a larger numbercalculations, which would increase the accuracy (by decreasing the errorassociated with interpolation) at the expense of expanding the size ofthe LUT.

[0042] Ultimately, the only unknown quantity of concern is temperature.Thus, in the preferred embodiment, the LUT comprises three columns ofintensity values and one column of corresponding temperature values. Tothat end, preferably a 4-dimensional look-up table (LUT) 162 is used todetermine temperature 164 from the three radiation signals. Of course,the LUT can be constructed in n-dimensions, corresponding to the numberof sensor signals used. The resultant table (LUT) is stored as adatabase (not shown) and is essentially formatted as plurality ofcolumns, one column for each wavelength chosen, and a final column ofcorresponding temperature values for each row of wavelengths, and isstored in memory (not shown). Referring again to FIG. 8, the threesignals 122 received from the signal conditioning stage are compared(e.g., using a search algorithm performed by, e.g., processor/controller106) to the corresponding intensity values created in the LUT, and acorresponding temperature value is obtained. The processor that receivesthe radiation intensity values and compares these values to the LUT maybe a separate processor without departing from the present invention.

[0043] Thus, it is evident that there has been provided a combustiontemperature sensor system and method for operating same that fullysatisfy both the aims and objectives hereinbefore set forth. It will beappreciated that although specific embodiments and methods of use havebeen presented, many modifications, alternatives and equivalents arepossible. For example, processor/controller 106, A/D converter 104, PGA102, D/A 116, and LUT (memory) 162 can be any custom made oroff-the-shelf components known in the art, and may be provided in oneunified system or be part of a modular, interchangeable system, providedthat the stated functionality is obtained. Although not shown, system 10can be adapted with appropriate I/O ports to permit, for example, thesignals to be displayed (e.g., using appropriately modified LCD and/orLED display modules) and to provide user-control of the variousoperational parameters herein described. To that end, the system 10 caninclude an RS485 digital bus to output the obtained temperaturecalculation to a display and/or mass storage (not shown). Furthermodifications are possible. For example, instead of the signalconditioning stage (FIG. 6) as provided herein, the signals receivedfrom the sensor 108 can be first fed into an A/D converter and suppliedto processor/controller 106 for conditioning. To that end, the signalscan be appropriately digitized at a sufficient sampling rate andbit-depth to achieve a desired resolution and dynamic range.

[0044] Still other modifications are possible. As described above inreference to the LUT, since each column of the table can be quite large(for example, 48×48×48), the LUT can be appropriately condensed, therebysaving memory space, and modified to optimize a sequential look-upoperation. While not wishing to be bound by example, theintensity-temperature table stored in the LUT may be modified asfollows. The first column of radiation intensity values can be arrangedin ascending (or descending) order, while keeping the correspondingvalues in the remaining columns in the proper row. The first k values ofthe first column are averaged to obtain 1 value; where k=n×n; and n isthe number of calculations made within the above-noted temperature andmolar concentration range. This is repeated n times. The first k valuesof column 2 are then arranged in ascending (or descending) order, andthe first n values are averaged, to obtain 1 value. The first n valuesin column 3 are then arranged in ascending order, and repeated. Ofcourse, the above process assumes three wavelengths and 1 temperaturevalue, in accordance with the preferred embodiment. However, thisprocess can extend to any given number of wavelengths calculated. Itwill also be apparent to those skilled in the art that the intensityvalues obtained by the sensor and those calculated in the LUT may notprecisely coincide. Thus, the present invention can be appropriatelymodified with standard interpolation techniques (e.g., linear, cubicspline, etc.). Alternately, the value of n may be increased so that thedistance between any two intensity values for a given wavelength iswithin error tolerances. In yet another modification, the LUT can bemodified to include a curve-fit polynomial expression ofintensity-temperature values, which can be approximated for eachintensity value obtained by the sensor.

1. In a system for measuring IR energies of a flame in a gas turbinehaving a combustion chamber and a turbine section, the improvementcomprising a lens for collecting infrared energy from that portion ofthe flame nearest to the inlet to the turbine section, said lensfocusing said infrared energy on one end of an optical fiber, said lensand optical fiber comprising sapphire, a mounting means for supportingsaid lens and the one end of the optical fiber in fixed relation to theflame, means for supplying compressed air to said mounting means toshield said mounting means and said lens from combustion gases in saidflame, means for positioning the other end of the optical fiber inposition to direct a beam of infrared energy transmitted by the fiberonto a plurality of infrared detectors positioned in a second mountingmeans spaced from the turbine, spectral separation means for separatingsaid infrared radiation into a plurality of different ranges of infraredfrequency and directing each of said ranges of infrared radiation ontoan associated detector, and optical chopping means for interrupting theinfrared beam at a predetermined frequency before it reaches said beamsplitter means.
 2. The system of claim 1 wherein said lens and opticalfiber mounting means are sealed, and the air is directed around thesealed mounting means.
 3. The system of claim 2 wherein said sealedmounting means is carried in a separate chamber which communicates withsaid combustion chamber through an opening in a wall of the combustionchamber and the compressed air enters said combustion chamber throughsaid wall opening to prevent combustion gases from entering saidseparate chamber.
 4. The system of claim 1, wherein said spectralseparation means comprises a plurality of narrow range infrared filters,each filter being positioned adjacent a separate and passing only anarrow range of infrared energy to its associated filter.
 5. The systemof claim 1, wherein at least one of said ranges of infrared energycorresponds to a peak CO₂ emission range and another corresponds to apeak H₂O range and a third corresponds to a peak background temperaturerange of infrared energy emitted from the combustion chamber walls. 6.In a system for measuring discrete IR energies of a flame in a turbinehaving a combustion chamber and a gas turbine section, the improvementcomprising a lens for collecting energy from that portion of the flamenearest the inlet to the turbine section, said lens focusing said IRenergy on one end of an optical fiber, said lens and optical fibercomprising sapphire, a mounting means for supporting said lens and theone end of the optical fiber in fixed relation to the flame, means forsupplying compressed air to said mounting means to shield said mountingmeans from combustion gases, means for positioning the other end of theoptical fiber in position to direct a beam of IR energy radiationtransmitted by the fiber onto a plurality of infrared detectorspositioned in a second mounting means spaced from the turbine, eachdetector having a filter means for passing a predetermined wavelength ofinfrared radiation to an associated detector, and optical chopping meansfor interrupting the infrared beam at a predetermined frequency beforeit impinges on said filter means, and means for controlling thetemperature of said detectors.
 7. The system of claim 6, wherein aportion of the fiber optic cable furthest removed from said lens isformed of chalcogenide (As₂S₃).
 8. The system of claim 2, wherein theair is fed circumferentially around the selected mounting means.
 9. Thesystem of claim 1, wherein the optical chopper operates at a frequencyon the order of 65 Hz.
 10. The system of claim 1, wherein said end ofsaid sapphire optical fiber is positioned in the focal plane of saidlens.